1. Field of the Invention
The present invention relates to an image forming apparatus of an electrophotographic process, such as a printer, a copying apparatus or a facsimile apparatus, having an air path for discharging, to the exterior of the apparatus, emission matter employed in the image forming apparatus.
2. Related Background Art
In lithographic printing, a coated paper is often used, in addition to a plain paper, as a recording material. Such a coated paper is formed by coating a surface of a bond paper with a chemical substance, in a glossy or a matted surface. Such coated paper is advantageously employed in color printing, and enables an image presentation having high definition and satisfactory color reproducibility.
On the other hand, in the field of image forming apparatus, such as a printer, a copying machine or a facsimile apparatus (but excluding a printing press utilizing ink), a high-definition image (fine-dot image) is requested, and, faithful color reproducibility is requested by the increase of color documents. For this reason, use of the coated papers is expanding.
When a coated paper is used in a printer or a copying apparatus, a volatile organic compound (VOC) may be generated by heat from the coated paper. Different from the printing press, the printer or the copying apparatus executes a heating process of about 180° C. in a fixing apparatus for fixing a toner image on the recording material, and such heat induces VOC generation from a chemical substance. It is desirable to remove such VOCs.
In the printer, copying apparatus, and the like, the air in the main body of the image forming apparatus is exhausted to the exterior from an exhaust portion, such as an air duct, through an adsorption filter. For example, Japanese Patent Application Laid-Open No. H02-273764 discloses a configuration of combining a catalyst filter and an adsorption filter, in order to decompose ozone of a high concentration.
On the other hand, the role of the adsorption filter is becoming more important in recent years, as a VOC removing filter. Such an adsorption filter is often based on porous active charcoal. Ozone or VOCs generated in the main body of the image forming apparatus is removed by adsorption in the active charcoal.
Since such an adsorption filter achieves gas removal by gas adsorption, it is necessary to increase the hermetic nature of the adsorption filter, in order to absorb VOC gas of a low molecular weight. Such a method can improve the efficiency of VOC removal of low molecular weight, but reduces a gas permeation from the interior to the exterior of the image forming apparatus, whereby the temperature within the image forming apparatus may be elevated, eventually, giving a detrimental influence on toner image forming means, which forms a toner image.
Also, when the VOC concentration becomes high, for example, by a continuous image formation, an increased removal efficiency for the removal of such VOCs lowers the gas permeability of the filter, thereby causing a temperature rise in the image forming apparatus.
On the other hand, such a temperature rise in the apparatus may be reduced by reducing the hermetic property of the adsorption filter in order to increase the gas permeation, but a part of the VOCs may remain without being adsorbed by the adsorption filter.
It is, therefore, desirable to increase the gas permeability while removing VOCs that may remain unabsorbed, without relying on an excessive hermeticity of the adsorption filter.